Liquid development of an electrical image in which a pulsating field is employed

ABSTRACT

A method of developing an electrical image or transferring an unfixed image in which the image is during development or during transfer subjected to a pulsating field with a fast attack and slower decay to repeatedly break the bonds tending to hold the developed image to a surface. A directional image field is used to control final settlement of the developer particles.

United States Patent Metcalfe et al.

The Commonwealth of Australia care of The Secretary, Department ofSupply. Parkes, Canberra. Australia Filed: Sept. 26, 1973 Appl. No:401,106

Assignee:

Foreign Application Priority Data Sept. 28. 1972 Australia 629/72 US.Cl. 96/1 LY; 96/1.4; 427/17 Int. Cl.'- G03C 13/10; 603G 17/00 Field ofSearch 96/1 R. 1 SD. 1 LY. 1 PE.

References Cited UNITED STATES PATENTS 3/1959 W'alkup 96/1 C 1/1963 Mott96/1 C 11/1966 Lehmann ..96/1SD X 7/1967 Gund1ach.... 96/1 SD X 9/1969Waly 96/1.3

1 1 Nov. 11, 1975 3.486.922 12/1969 Cassiers et a1 427/15 3.515.5486/1970 Lange 16/1 R 3.560.203 2/1971 Honjo et a1 96/1 LY 3.576.6234/1971 Snelling 96/1 LY 3.657.091 4/1972 Forest 96/1 PE X 3.759.2229/1973 Maksymiak et a1 96/1 SD X 3.784.397 1/1974 52110 et al. 96/1 LY X3.804.510 4/1974 Sato et a1. 96/1 LY X 3.811.764 5/1974 Forest 96/1 PE XFOREIGN PATENTS OR APPLICATIONS 796.679 10/1968 Canada 96/1 LY 267.3415/1964 Australia 96/1 LY 281.765 4/1966 Australia 96/1 LY 1.214.15512/1970 United Kingdom 96/1 LY 1.165.038 9/1969 United Kingdom 427/152.112.015 10/1971 German 96/1 LY 7.005.615 10/1970 Netherlands 96/1 LY7.005.938 10/1970 Netherlands 96/1 LY Primary E.\'amt'net'Charles L.Bowers. .lr.

Assistant Examiner-John R. Miller Attorney. Agent, or Ft'rntHaseltine.Lake 8.: Waters 1571 ABSTRACT A method of developing an electrical imageor transferring an unfixed image in which the image is duringdevelopment or during transfer subjected to a pulsating field with afast attack and slower decay to repeat edly break the bonds tending tohold the developed image to a surface. A directional image field is usedto control final settlement of the developer particles.

9 Claims, 2 Drawing Figures U.S. Patent Nov. 11, 1975 GE N m w W @FJ W mA 1 n F u m Q .L m .i l. 1.. a

LIQUID DEVELOPMENT OF AN ELECTRICAL IMAGE IN WHICH A PULSATING FIELD ISEMPLOYED This invention relates to methods of and means for developingand transferring images otherwise developed. The invention is usablewith electrical images produced in any way but particularly to what areknown as chargeless" processes.

BACKGROUND OF INVENTION According to the normal methods of developingimages, such as latent electrostatic images produced by applying adeveloper to a photoconductive membrane on which an image has beenformed by charging and light bleeding, certain difficulties haveoccurred during the application of a developer, either in the form of adry powder carried on granules or the like, or a toning medium suspendedin an insulating liquid.

Among these problems are the contamination of the background areas wheredeposition should not take place, and also the attainment of therequired densities and correct shade values in, for instance, continuoustone methods, and such effects as edge intensification adds to theproblem of development, particularly with what are known as drydevelopers. When it is desired to transfer an image from an area whereit was developed, which is usually achieved while the image is still inan unfixed or a wet condition, complete transfer of the image is usuallynot achieved, and also during the transfer there is a tendency to losedefinition in the image, and to overcome this it has been proposed topass a field, including an alternating biased field, through the imagein a direction such that the developed image is forced away from thephotoconductive membrane on which it was made and on to the sheet onwhich the image is subsequently fixed, either by a heat fusion or byevaporation of the carrier liquid or by other means. The art is taught,for instance, in (1.8. Pat. No. 3,464,8l8 The art of using alternatingcurrent with a bias for development is taught in US. Pat, Nos. 3,657,091and 3,811,764.

In the case of chargeless processes, that is a process in which asurface simply receives patterned rays which then leave a differentialeffect or differential dielectric constant on the surface capable ofbeing developed, a further problem exists in that the magnitude of thedifferential variation is relatively low compared to what ,can beachieved by charging and then light bleeding, and this lower image valuehas resulted in the problem that only very fine developers could be usedbecause coarser developers would not move effectively, or be retained,on the weaker latent images which thus result. Even with fine developersthere has been the problem that densities are relatively low andtherefore heavy deposits of developer cannot be achieved, and one of theprinciple objects of the present invention is to provide a method of andmeans for developing improved images, particularly, though notexclusively, images on what are known as the chargeless system.

It can be mentioned at this stage that the chargeless system wasdeveloped largely to overcome artifacts which are caused through unevencharging according to the methods used at present. and many forms ofcharging have been devised to try and overcome this irregularity in thecharge on the photoconductor which then, of course, is reproduced in thedeveloped image.

Such a chargeless process was disclosed in Australian Patent No. 243,184in the name of The Commonwealth of Australia the basic applicationhaving been lodged on the 5th Mar. 1959.

It follows also that chargeless images require advanced techniques totransfer them, because of the lower image density which has in the pastbeen obtainable, but this is also true of normally produced imagesincluding dry developed images, and the present invention is directed toproviding a better form of transfer for any of the known systems.

SUMMARY OF INVENTXON We have discovered that much more effectivedevelopment of images can be obtained by any of the known systems,including the chargeless system, if during development, and also duringtransfer if this is required, a pulsating field with fast attack andslower decay is applied to the area where the development is takingplace, or while the transfer is being effected.

The pulsating field is preferably such that a saw-tooth wave is producedwhich has a sharp leading edge and a trailing decay portion, so thateach impulse reaches a maximum when first initiated and then dies awayto the next impulse, the frequency depending on the developer and theconditions and results required. The frequency may be in the order of 50cycles to many thousands of cycles, although when the developer isapplied by roller or the like it is preferred to have a high frequency,preferably in excess of a few thousand cycles, as otherwise it is foundthat the traversing of the developer roller across the surface, whichroller is energised to apply the impulses, will result in transversemarkings varying in intensity between pulses.

The concept of the invention is that because of Van der Waals forceswhich exist on the developer particles as they are deposited on thesurface, the pulsating field causes the particles hold to be broken sothat they do not simply deposit on the surface and remain there, but arein a state of agitation so that an image is repeatedly built up and atleast partly destroyed, the interesting phenomenon being that duringthis action the developer particles are kept in motion at the interfaceof the surface being developed and, therefore, are able to deposit verymuch more heavily than would otherwise be possible. It is assumed thatthis is because the particles already deposited do not necessarilyshield the area, but rather as all particles are oscillating there canbe an extensive build up at even a low charge area as this area is noteffectively covered until such time as development is completed, whichoccurs after a required time when the pulsating field is removed. Atthis stage the particles settle down and remaining in position. The sametheory applies when the developer particles are to be transferred fromthe membrane on which they have been deposited because here again thesharp pulsations ensure that the hold of the particles on the surface isbroken by the pulsation, and therefore the Van der Waals forces arecountered by this action, and it is assumed that this is the reason whya better transfer of the particles is then possible because duringtransfer their effective attraction to the surface on which they arefirst deposited is lessened and, because of the agitated conditionsunder which they are transferred, the particle can be packed much moreeffectively on the receiving sheet. Extensive tests have shown that evenwith chargeless development of images, high densities can be obtained,not only by using ultra-fine developer particles but we have found thatwhen the pulsating field is present, also relatively coarse developers,with extensive depth of cover of developed areas, can be achieved.

The theory which we believe to be applicable is that under normaldeveloping conditions, particularly where the field strength of thelatent image is relatively low, particles deposit under this field andthen shield the area and prevent further developer particles moving tothe latent image, but when the pulsating current is applied. the Van derWaals forces which tend to hold the particles in place and together arebroken, and the particles thus can be packed in a more consolidated formand to a greater depth.

So far as the direction of the pulsating field is concerned in relationto the developer particles, we have found that this can vary accordingto conditions, and in the case of transfer is preferably in thedirection which tends to move the particles on to the receiving surfaceand away from the surface on which the image was formed, but it will berealised that because of the pulsations and the somewhat slower decay,the first action will probably be to break the Van de Waals forces, butas the pulse decays the particles can move back again but with asomewhat lesser intensity effect because of the decaying field, and thistype of wave, therefore, would seem to produce a movement in onedirection although during the movement the particles may be pulsatingquite extensively. The effect has been found to be quite different tothat which exists where a constant field is used to try and moveparticles from one surface on to another.

in the case of development, the field is preferably again in the samedirection so that during the pulsations the Van de Waals forces on theparticles as they near the surface and before they reach a balance arerepeatedly repulsed so that, while they are drawn by the field to settlein a particular position of the image, their movement is of a pulsatingnature so that they cannot immediately attach but are kept in anagitated state adjacent to an area where they will finally be allowed todeposit when the pulsating field is removed or countered.

While we do not wish to be bound to the basic theory set out above, itshould be remembered that according to the Van de Waals force theory,electrons in a cloud of negative electricity in a molecule are in rapidmotion, and the charge distribution may therefore be thought of asfluctuating in time.

The hold actually occurs at any instant in that the dipole in onemolecule will cause an electric field to act on a neighbouring moleculeand this will disturb the motion of the electrons in the secondmolecule, and it is the interaction of the two dipole movements whichresult in the holding force which tend to keep the molecules of thedeveloper locked to the surface on which such a developer has beendeposited, and to each other and while the electron cloud keeps themolecules from actually contacting the surfaces, an equilibrium existswhich it is the purpose of the present invention to upset by means ofthe pulsating current applied to the developer particles at the sitewhere they are deposited.

The Van de Waals force, of course, varies with particle size but can bemany times the force of gravity, but nevertheless the introduction ofthe pulsating current, which can be applied by a roller or an electrodethrough the membrane on which development is being effected causes thebetter development or transfer to be effected, an electrode on the backof this membrane, completing the circuit, or the field may be applied toa conductive layer on the membrane on which the photoconductor issupported, a second electrode of course being then used on the developerside somewhat remotely from the area of deposition. The method ofapplying the field is not important so long as it is present at theinterface being developed or from which the developer is beingtransferred.

The pulsating field can be biased to be above or below earth potentialto impress a constant field on it acting in one direction, and it willbe realised that this allows an undirectional biasing effect to beobtained as well as the superimposed pulsating direct current.

In order however that the invention may be more fully appreciated anembodiment of mechanism for carrying out the invention which wasdeveloped during research is now to be described but it is to be clearthat the invention need not necessarily be limited to this.

In the FIG. 1 embodiment a variable frequency power supply 1 isconnected to the primary of a transformer 2 by means of a wave shapingtriac 3 operating under control of an i.c. phase control unit 4 toproduce at the secondary S of the transformer unit 2 pulses which arethen rectified by the diode 6 and filtered if necessary by the filtercircuit 7, the resulting pulsating current being then applied throughthe centre tap of the resistor 8 to a developer roller 9 which has thesheet 10 containing the latent image passed between it and a pressureroller 11 which as shown is connected to earth. The potential can beregulated by adjusting the potentiometer 12.

A filter 13 prevents radiation from the triac 3.

14 indicates in dotted lines a receiving sheet when the device is usedfor transfer purposes in which case the roller 9 is merely a pressureroller to apply the bias as the sheet 10 will have been previouslydeveloped and the developed sheet is then pressed against the sheet 14to transfer the image from the sheet 10 to the sheet 14.

The FIG. 1a diagrams 15, 16 and 17 show the form of output which can beachieved, the positive pulses being of course shaped by the phasecontrol 4 in known manner to cut required parts of each cycle to givethe necessary type of agitation to the particles. The pulses can have apositive or negative characteristic by appropriately positioning therectifying diodes 6 so that direc tional effects can be obtained.

As an analogy in the present case attention could be drawn to the biasused during tape recording where the bias made possible highly effectiverecording which would not be obtainable without a bias, the theory ofoperation in that case being that the oscillation keeps the magneticorientation in a mobile state to thereby allow a relatively small signalto give the correct orientation to the particles.

In the case of the present invention of course the analogy is notidentical but the general principle of having the developer particles ina state of agitation when they are subject to the image field appears tohave advantages as significant as was the advantage of using bias inmagnetic tape recording, and the results obtained by this method were byno means obvious because in the one case a magnetic orientation wasinvolved whereas in the present case a physical displacing action ofparticles is necessary.

It will of course be quite obvious to anyone versed in the art thatwhere there is relative movement between a developer roller and amembrane containing a latent electrostatic image being developed, or twomembranes when transfer is being effected, the frequency must be suchthat the characteristic of the applied pulcming 4 sating current is notreflected in the deposition of the Jordosol 2232/50 developer, andobviously also relative motion is not 5 shriilalkydfesln 400 grams(Jordon Chemicals) necessary because the invention can be applied tozinc oxide other forms of development using a biasing plate adja-(colloidal g 1200 slams (Durham) cent to the area where development istaking place so Bromoscresol Green 0.5% by wt. in methyl alcohol thatthe invention applies to any form of development to milliliters of t f rI Bromophenol Blue 0.5% by wt. in methyl alcohol 10 milliliters Thefollowing examples are given to indicate types of Sodium Fluomcein 1% byM in "mm alcohol developer and field strength. l0 milliliters ErythrosinB. 1% by wt. in methyl alcohol 10 milliliters EXAMPLES OF COATINGSCobalt Naphthenate Electrophotographic coatings may be produced as ZincNapthenate Solvent 6% solution 0.1 grams 3% solution 1.0 grams followsi(Esso) Also! 95/[30 2.000 milliliters Coating Mowiml polyvinyhbmym (860m70 grams 0 These materials are ball milled together to fonn an (Hoechst)V electrophotographic composltion.

Zinc oxide colloidal grade 350 grams (Durham Chemicals) Coating 5 TheMowital was taken up in 500 mls. acetone and 50 ax:523 (Myviny' 100grams mls. methyl ethyl ketone, and ball milled with the zinc zi oxidespecial 1 grade I000 grams oxide. Durham) This coating can be applied toeither film, metal backing or paper.

The Mowital was taken up in 800 millilitres of methyl ethyl ketone and200 millilitres of methyl alcohol, and

Coming 2 ball milled with the zinc oxide which was previouslylsojordosol 4501/60 short oil alkyd resin 430 grams dyed with thefollowing! (Jordan Chemicals) 2' 'd ll d l ti Tgm zff o a an e) .58 armsSodium Fluorescein l.0% solution in methanol Rose Bengal (sensitiserdye) 0.2 grams l0 mlllll tels Toluol i200 millilite rythr sm 3 L0)solutlon in methanol 5 milliliters Rose Bengal LO'k solution in methanol2 milliliters Bromocresol Green 0.5% solution in methanol 40 5milliliters Bromopllenol Blue 0.5% solution in methanol 5 millilitersThese materials were ball milled together to form a coating composition.

Cobalt and zinc naphthenate driers were added (0.5% and 0.5% by wt. ofsolid resin).

This coating composition was let down with 500 millilitres of methylethyl ketone solvent and 500 millilitres of perchlorethylene to form thefinal coating composition.

Coating 3 45 Styrene-butadine copolymer Esso polymer 200 "i' EXAMPLES OFDEVELOPMENT Zinc oxide 500 grams Lead naphthenate 6% solution in mineralspirits l.0 gram Cobalt naphthenate 6% solution in mineral spiritsDeveloper 1 Developer 100 grams Kohinoor Carbon Black Zirconium octoate6% solution tn mineral spmts 300 "um sunflower ed on (Manna) l '9" 500grams a.r.v. oil (Visoostatic) (British Petroleum) Cerium octoate 6%solution In mineral spirits 20 mam alkyd resin 0.5 gram Solvent Also!95/130 900 milliliters Emma Toluol v 65 milliliters Hexyl acetate l0milliliters 5321.2? :g Dispersed in 1000 mls. lsopar G. With thisdeveloper Pentoxone 5 milliliters a pulsating repelling direct currentof 200 volts was Disulphine Blue Acridine Orange conductive layer.

l'lb by wt in methyl alcohol 2 milliliters I'll by wt. in methyl alcohol2 milliliters Erythrosin B l% by wt. in methyl alcohol 2 milliliters rSodium fluorescein 5 milliliters These materials are ball milledtogether and dip coated on paper, metal, wood, or film base to form aphoto- De Z Copolymeric Blue Developer Hoechst) I00 grams Hostapenn Blue836 200 grams Styrene butssliene copolymer e.g. "Solprene 1205"(Phillips Imperial Chemical) -continued Developer 2 Copolymeric BlueDeveloper Developer 7 I grams Vinyl toluene- 40 grams Permanent yellow00 (Hoechst) acrylate copolymer l0 grams Solprene I205 "Pliolite VTAC(Australian Synthetic Rubber) 7 t VTAC Dispersed in I00 mls. Esso I00I000 mls. lsnpar E The copolymeric resin were taken up in Solvesso I00and subsequently milled with the blue pigment and a repelling fieldsimilar to that used in the preceding example was used.

Developer 3 (Copolymeric suspension in lsopar E (Esso). andisoparaffinic hydrocarbon solvent) Isopar E "Solprene I 205 200 mls. 5grams (solution of I gram of solid in 2 mls.)

"Pliolite VTAC 5 grams (solution of 1 gram of solid in 2 mls.)

0.1 parts by wt.

The developer can be applied by a simple electrode or by a roller.

A pulsating repelling bias at 200 volts was used at 50 cycles per secondwith the roller moving at 30 centimetres per second. Additionaldevelopers are as follows:

Roller pass 250 volts at 100 to I000 cycles at 20 centimeter per second,pulsating repelling D.C.

Developer 5 BIA/8 54 grams Hostlperm Blue B30 (Hoechst) 6i gramsSolprene I205 32 grams VTAC. Dispersed in I00 mls. Esso I00 I000 mls.Isopar E Roller pass l0 volts at I0 centimeter per second with a pulsefrequency of $0 to 200 cycles per second.

Developer 6 Yellow 40 grams Graphtol yellow 48I3 0 (Sudan) 20 gramsSolprene I205 I0 grams VTAC. Dispersed In 100 this. Esso I00 i000 mls.Isopsr 5 Roller pass 500 volts at 20 centimeter per second pulsatingrepelling D.C. at a cycles per second.

frequency of 50 to 5000 Roller pass I00 volts at I5 centimeter persecond A.C. at 50 cycles without directional effect other than the imagefield.

Developer 8 60 grams Graphtol Red I630 l0 grams Solprene I205 I0 gramsVTL Copolymer Dispersed in I00 mls. Esso I00 I000 mls. lsopar E Rollerpass 50 volts at 20 centimeter per second pulsating repelling D.C. 50 to500 cycles.

Developer 9 50 grams Isol Ruby Red grams Brillflst Rose Red 30 20 gramsPale lowering Lithographic Varnish 200 grams Rhodene alkyd resin L42/70Dispersed in I00 mIs. Esso 100 I000 mls. lsopar E Roller pass 50 voltsat 10 centimeter per second pulsating D.C. or A.C. at 50 to 5000 cyclesper second.

Developer I0 50 grams Isol Ruby Red 30 grams Brillfut Rose Red I50 gramsAlkyd Resin P470 12 grains Beeswax 15 grams Toluene Dispersed in 45 I00mls. Esso I000 mls. llopar E Roller pass 20 volts at 10 centimeter persecond, AC. at I00 cycles per second.

Developer II 100 grams Aluminum bronze metal powder 20 grams Alkyd ResinP470 I5 mls. Toluene Dispersed in $0 mls. Esso I00 I000 mIs. Isopar GRoIIerpass 200 volts at 20 centimeter per second AC. or pulsating D.C.at 50 to 500 cycles per second.

Developer I2 In example 9 the aluminuium bronze metal powder is placedby silver, zinc, aluminium, iron, chromium, copper, tin or other metalpowder Roller pass 200 volts at 20 centimeter per second.

A.C. or pulsating D.C. at 50 to I000 cycles per second.

In coating 1 the operating voltage can" be reduced to half that for thelower dielectric constant binder coating of Examples 2 and 3. The reasonwhy alternating current can be used is as said because the coatings arethemselves rectifying.

Any of the above examples can be transferred before fixing by applying adirectional pulsating voltage of between l and 200 volts at a frequencyof to 5000 cycles. I

IDENTIFICATION or TRADE MARKS AND TRADE NAMES BUTON 200,styrene-butadiene copolymer made by Esso.

B.P.V. OlL synthetic automotive lubricating oil containing antioxidantZDP", dialkyl zinc dithiophosphate in solution, made by BritishPetroleum Ltd. BRILLFAST ROSE RED 4444, a red phosphotungstomolybolicacid toner.

Coates hydrocarbon dispersible flake black comprises pure carbon blacktogether with ethyl hydroxy cellulose resin.

B580 100 Solvent is a hydrocarbon solvent supplied by Esso ChemicalsAustralia Limited, having an aromatic content of 98%, flash point ofI08F., and distillation range l59-l82C.

ELVACITE RESIN is an acrylic resin manufactured by DuPont, Delaware,U.S.A.

B880 100 is an aromatic hydrocarbon solvent with 98% aromatics, KB Value9', final boiling point 182 C. GRAPI-ITOL BLUE BLF, phthalocyanine blue,C.I. pigment blue made by Sandoz.

I-IOSTAPERM BLUE 83G copper phthalocyanine blue, pure beta-form, made byHoechst C.l. pigment Blue 15, Colour Index No. 74l60. A ISOJORDOSOL450ll60 short oil alkyd resin made by Jordan Chemicals.

ISOL RUBY RED BKS 7520 (KVK) a lithol ruby red C.I. Pigment Red 57,Agfa, Calcium lake.

ISOPAR G a hydrocarbon liquid solvent with greater than 95%isoparaffinic content, and aromatics and olifins less that l percent,and remainder cycloand normal parat'fins, KB No. 27, final boiling point177C. ISOPAR E a hydrocarbon liquid solvent with greater than 95%isoparaffinic content, aromatics and olifins less than 1 percent, withremainder cyclo and normal paraffins, KB Value 29, find boiling pointI43C. KOI-IINOOR CARBON BLACK supplied by A.C. Hattriclt Ltd. Aust.SUNFLOWER Seed Oll vegetable oil supplied by Meggitts Ltd., Australia.

MOWITAL B601! polyvinyl butyral resin, made by Heechst, Germany;containing polyvinyl seats] 76-?! percent polyvinyl acetate 1 percentand polyvinyl alcohol 10-21 percent.

MICROLITH Pigments comprise a pigment and a resinous carrier. MicrolithBlack pigment contains pure neutral carbon black together with a toluenesoluble carrier resin such as Stabilite Ester l0 of the Hercules PowderCo., U.S.A.

MICROLl'll-I BLUE 46'! comprises a stable phthalocanine blue pigmentwith a greenish cast to- .gether with Stabilite Ester l0 resin. ColourIndex 74l60 MICROLITH GREEN GT comprises a medium shade ofphthalocyanine green together with Stabilite Ester l0 resin, themicrolith pigments are manufactured by Ciba Co., Switzerland, ColourIndex 1245s.

10 PLIOLITE SSD is a styrene/butadiene copolymer. KB value 60,manufactured by Goodyear Corp., U.S.A. PLIOLITE V.T.A.C. is a vinyltolucne/acrylate copolymer. KB value 36. PERMANENT YELLOW 66 extra, adiazo yellow pigmerit without lake forming groups, G]. pigment yellow17, colour Index No. 21105. PENTACITE P423 is a modified pentarethyritolester resin with acid number 20-30. PLIOLITE VT RESIN is astyrene/butadiene type copolymer rubber made by the Goodyear Corp., USA.and prepared by the G.R.S." method in which the butadiene polymerises inthe main by a 1,4-addition. Pliolite VT is a vinyl toluenelbutadienerandom copolymer rubber, soluble in mineral spirits. PALE LOWERINGLITHOGRAPI-IIC VARNlSl-I a polymerized linseed oil varnish made byMeggitts Ltd., Australia, Polylin acid value 40-65 viscosity 7.0-9.5poises at 25C, from alkali refined linseed oil. RHODENE RESIN L42/70, asafflower oil modified alkyd resin made by Polymer Corporation,Australia, acid value 6-10 with 69-7 1 percent solids, 64% oil length.SOLPRENE i205, styrene-butadiene copolymer Phillips Petroleum Corp.,U.S.A., a block copolymer of hutadiene and styrene in the ratio /25containing 97.5 percent of rubber hydrocarbon, A.S.T.M. No. I205 withmajority of styrene molecules added as polystyrene at the end of a longchain of butadiene units. SUPERBECKOSOL 1352/60, a semi-drying saffloweroil isophthalic-modified long oil alkyd resin with 59-61% non-volatilematter, acid value 3-6, oil length 60%, viscosity Gardner I-Ioldt Y-Z.VlNYLlTE VYNW, a vinyl chloride-acetate resin, approximate compositionvinyl chloride 97%. vinyl acetate 3%, and specific gravity L39.

What is claimed is:

l. The method of developing an electrical image defined by changes ofdielectric constant on a photoconductive surface comprising; subjectingthe image, in the presence of a liquid developer comprising developerparticles suspended in an electrically insulating liquid to a pulsatingfield having a polarity and intensity to repeatedly break the bondscaused by the Van de Walls forces as the developer particles are drawnto an image area during development, controlling the said pulses tomaintain the said developer particles in oscillation during development,but maintaining the electrical image field during development to give adirectional component to the particle movement to settle the saidparticles on the image areas. said pulsating field having a fast strongdislodging force followed by a slower decay whereby the particles afterdislodgement have time to resettle under the said electrical imagefield.

2. The method of claim 1 wherein the pulsating field is produced byphase control cut off of a rectified pulsating current.

3. The method of claim 1 wherein the pulsating field is a direct currentfield.

4. The method of claim 1 wherein the pulsating field is an alternatingcurrent field.

5. The method as claimed in claim 1 wherein the photoconductive surfaceis coated with a coating of polyvinyl-butyral and colloidal grade zincoxide, the polyvinyl-butyral being taken up with acetone andmethylethyleltetone and ball milled with the zinc oxide and applied to asupport.

3 ,9l 8,966 l l 12 6. The method as claimed in claim 1 wherein the pho-8. The method as claimed in claim 1 wherein the photoconductive surfaceis coated with a coating formed of toconductive surface is coated with acoating formed of short oil alkyd resin, colloidal grade zinc oxide,sensishort oil alkyd resin, zinc oxide, coloring material, sotizer die,and toluol, which are ball milled together to dium fluorescein,naphthenate and a solvent, all ball form a coating composition to whicha dryer is added. milled together to form an electrophotographic compo-7. The method as claimed in claim 1 wherein the phosition coated on asupport. toconductive surface is coated with a coating formed of 9. Themethod as claimed in claim 1 wherein the phostyrene-butadine copolymer,zinc oxide, lead naphtoconductive surface is coated with a coatingformed of thenate, cobalt naphthenate, zirconium octoate, ce- '0polyvinyl butyral and zinc oxide which are taken up in riurn octoate, asolvent, toluol, acetate, butanol, penmethylethylketone and methylalcohol and ball milled toxone, and coloring material, all ball milledtogether with sodium fluorescein and coloring material to form andcoated onto a support to form a photoconductive a coating compositionwhich is deposited on a support. layer. 4- a: w In

1. THE METHOD OF DEVELOPING AN ELECTRICAL IMAGE DEFINED BY CHANGES OFDIELECTRIC CONSTANT ON A PHOTOCONDUCTIVE SURFACE COMPRISING: SUBJECTINGTHE IMAGE, IN THE PRESENCE OF A LIQUID DEVELOPER COMPRISING DEVELOPERPARTICLES SUSPENDED IN AN ELECTRICALLY INSULATING LIQUID, TO A PULSATINGFIELD HAVING A POLARITY AND INTENSITY TO REPEATEDLY BREAK THE BONDSCAUSED BY THE VAN DE WALLS FORCES AS THE DEVELOPER PARTICLES ARE DRAWNTO AN IMAGE AREA DURING DEVELOPMENT, CONTROLLING THE SAID PULSES TOMAINTAIN THE SAID DEVELOPER PARTICLES IN OSCILLATION DURING DEVELOPMENT,BUT MAINTAINING THE ELECTRICAL IMAGE FIELD
 2. The method of claim 1wherein the pulsating field is produced by phase control cut off of arectified pulsating current.
 3. The method of claim 1 wherein thepulsating field is a direct current field.
 4. The method of claim 1wherein the pulsating Field is an alternating current field.
 5. Themethod as claimed in claim 1 wherein the photoconductive surface iscoated with a coating of polyvinyl-butyral and colloidal grade zincoxide, the polyvinyl-butyral being taken up with acetone andmethylethyleketone and ball milled with the zinc oxide and applied to asupport.
 6. The method as claimed in claim 1 wherein the photoconductivesurface is coated with a coating formed of short oil alkyd resin,colloidal grade zinc oxide, sensitizer die, and toluol, which are ballmilled together to form a coating composition to which a dryer is added.7. The method as claimed in claim 1 wherein the photoconductive surfaceis coated with a coating formed of styrene-butadine copolymer, zincoxide, lead naphthenate, cobalt naphthenate, zirconium octoate, ceriumoctoate, a solvent, toluol, acetate, butanol, pentoxone, and coloringmaterial, all ball milled together and coated onto a support to form aphotoconductive layer.
 8. The method as claimed in claim 1 wherein thephotoconductive surface is coated with a coating formed of short oilalkyd resin, zinc oxide, coloring material, sodium fluorescein,naphthenate and a solvent, all ball milled together to form anelectrophotographic composition coated on a support.
 9. The method asclaimed in claim 1 wherein the photoconductive surface is coated with acoating formed of polyvinyl butyral and zinc oxide which are taken up inmethylethylketone and methyl alcohol and ball milled with sodiumfluorescein and coloring material to form a coating composition which isdeposited on a support.